A vehicle may include a heat pump to adjust environmental conditions of a vehicle's passenger compartment. The heat pump may operate in several different modes to control the vehicle cabin environment. For example, the heat pump may be operated in a heating mode where thermal energy is transferred from the heat pump to coolant that warms the vehicle cabin. The heat pump may be operated in a cooling mode where a heat exchanger in the vehicle's cabin operates as an evaporator to cool air that passes over the interior heat exchanger. The heat pump may also operate in a de-humidification mode where the heat pump cools passenger cabin air to remove humidity and then warms the air to heat the passenger cabin or defrost vehicle windows.
The ability to operate the heat pump in more than one mode increases the utility of the heat pump. However, operating the heat pump in more than one mode may make controlling the heat pump more challenging. In particular, it may be possible for the heat pump's compressor to flow less refrigerant and lubricant during some operating conditions of the heat pump's different operating modes. For example, compressor lubrication may be reduced due to high pressure ratios across the compressor when a heat pump is operated in a heating or dehumidification mode where an exterior heat exchanger operates as an evaporator and compressor inlet or suction pressure is driven by ambient temperature. The reduced flow of compressor lubricant may increase the possibility of heat pump compressor degradation. Therefore, it may be desirable to provide a way of operating the compressor in the different heat pump modes so that heat pump compressor lubrication may be ensured.
The inventors herein have recognized the above-mentioned disadvantage and have developed a vehicle system, comprising: a refrigerant loop including a compressor; a first pressure sensor; and a controller including executable instructions stored in non-transitory memory to adjust a speed of the compressor in response to a pressure ratio across an outlet of the compressor and an inlet of the compressor, the pressure ratio based at least in part on output of the first pressure sensor.
By controlling heat pump compressor speed in response to a pressure ratio between a heat pump compressor inlet and a heat pump compressor outlet, it may be possible to provide the technical result of reducing the possibility of heat pump compressor degradation. In particular, the possibility of heat pump compressor degradation may be reduced when the heat pump is operating in a heating mode or dehumidification mode where heat pump compressor inlet pressure may vary substantially. If the pressure ratio between the heat pump compressor inlet and outlet increases beyond a threshold, compressor speed may be reduced to increase refrigerant and lubrication flow through the compressor. As such, the possibility of compressor degradation may be reduced. If the pressure ratio increases sufficiently, the compressor may be stopped based on a recognition that compressor lubrication decreases as refrigerant and lubricant flow through the heat pump compressor decreases at higher pressure ratios across the compressor.
The present description may provide several advantages. For example, the approach may reduce the possibility of heat pump compressor degradation. Further, the approach may be provided without a significant increase in system cost. Further still, the approach may be applied to a variety of system configurations to provide similar functionality in a variety of different systems.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.